Wideband extension of telephone speech for higher perceptual quality

• US 20020193988A1
• Filed: 07/03/2002
• Published: 12/19/2002
• Est. Priority Date: 11/09/2000
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Gerrits, Andreas Johannes, Sluijter, Robert Johannes, Chennoukh, Samir
• Granted Patent: US 7,346,499 B2
• Time in Patent Office: Days
• US Class Current: 704/205
• CPC Class Codes: G10L 21/0364 for improving intelligibility
• CPC Class Codes: G10L 25/24 the extracted parameters being the cepstrum

Abstract

Wideband extension of telephone speech for higher perceptual quality. A method for extending the frequency range of a speech signal using wideband extension method with an inverse filter and a synthesis filter where both filters receive LPC coefficients from an LPC estimator. The wideband LPC coefficients are obtained from wideband LSFs. The wideband LSFs are obtained by appending highband LSFs, created by applying a matrix to narrowband LSFs, and lowband LSFs, created by dividing the narrowband LSFs by two. The matrix used to create the highband LSFs is selected from a predetermined list of matrices. The selection is based on either wideband or narrowband reflection coefficients extracted from the narrowband speech signal.

Claims

1. Method for extending line spectral frequencies of a narrowband speech signal with a frequency range to line spectral frequencies of a wideband speech signal comprising a highband frequency range and the frequency range of the narrowband speech signal comprising the steps of

Deriving line spectral frequencies for the highband frequency range of the wideband speech signal by applying a matrix obtained by training to line spectral frequencies of wideband speech signals in the frequency range of the narrowband speech signal, t the line spectral frequencies of the narrowband speech signal

Mapping the line spectral frequencies of the narrowband speech signal to line spectral frequencies of the wideband speech signal in the frequency range of the narrowband speech signal

Combining the line spectral frequencies for the highband frequency range with the line spectral frequencies of the narrowband speech signal.

2. Method for extending line spectral frequencies of a narrowband speech signal according to claim 1, characterized in that the matrix is selected from a list of predetermined matrices based on reflection coefficients obtained from the narrowband speech signal.

3. Method for extending line spectral frequencies of a narrowband speech signal according to claim 1, characterized in that the matrix is selected from a list of predetermined matrices based on reflection coefficients obtained from wideband linear prediction coefficients.

4. System for extending the frequency range of speech signals at an input comprising an output and an upsampler connected to the input of the system and an input analysis means for determining linear prediction coefficients and reflection coefficients, an input of the input analysis means connected to the input of the system, the upsampler comprising an output connected to an input of a first filter, which first filter comprises an output and is arranged to filter based on linear prediction coefficients, the output of the first filter connected to a an input of a spectral folding means with an output connected to an input of a second filter comprising an output, which second filter is arranged to filter based on the linear prediction coefficients, the output of the second filter being connected to the output of the system for extending the frequency range of speech signals, caracterized in that an output of the input analysis means, which input analysis means is operative to provide line spectral frequencies of the speech signals at the input of the input analysis means, is connected to an input of a multiplier, which multiplier is operative to multiply the line spectral frequencies of the speech signals by two and provide the line spectral frequencies multiplied by two to an array appender and to a highband LSF estimator, where the array appender is operative to append highband LSFs as provided by the highband LSF estimator to the line spectral frequencies multiplied by two, the array appender comprising an output connected to an input of a linear prediction coefficient determinator comprising an output for providing linear prediction coefficients to the first filter and the second filter.

5. System for extending the frequency range of speech signals according to claim 4, characterized in that the highband LSF estimator is arranged to determines the highband LSFs by applying a matrix to the line spectral frequencies multiplied by two.

6. System for extending the frequency range of speech signals according to claim 5, characterized in that the system is oprative to select the matrix from a predetermined list of matrices.

7. System for extending the frequency range of speech signals according to claim 6, characterized in that the system is operative to select the matrix based on reflection coefficients obtained from the narrowband speech signal.

8. System for extending the frequency range of speech signals according to claim 7, characterized in that the system is operative to select the matrix based on reflection coefficients obtained from wideband LPC coefficients.

9. Mobile telephone comprising a system for extending the frequency range of speech signals according to claim 4.